Petrography and physical-mechanical evaluation of mafic-ultramafic rocks from Atud-Um Khasila, Egypt for dimension stone

Abstract

This study investigates the petrography, physical, and mechanical properties of mafic-ultramafic rocks from the Atud-Um Khasila region in Egypt's Central Eastern Desert for dimension-stone applications. Eighteen representative samples of metagabbro, olivine gabbro, and serpentinite were analyzed using integrated petrographic and geotechnical methods. Standard ASTM and EN procedures were utilized to determine bulk density, water absorption, apparent porosity, and uniaxial compressive strength (UCS). Additionally, serpentinite samples were evaluated for durability against salt crystallization and thermal shock. Petrographic analysis reveals that gabbroic rocks (metagabbro and olivine gabbro) comprise plagioclase, amphibole, pyroxene, and olivine, forming interlocking textures that may contribute to their strength. Metagabbro demonstrated high strength (74.6 MPa), low porosity (0.24%), and minimal water absorption (0.08%). Olivine gabbro also performed well, with a strength (76.8 MPa), a porosity (0.29%), and water absorption (0.11%). In contrast, serpentinites, mostly made up of antigorite, talc, and carbonate veins, showed lower strength (67.3 MPa) due to alteration but had weight losses below 1% during testing. Overall, gabbroic rocks are appropriate for dimension stone applications, while serpentinite does not meet ASTM standards. This study demonstrates that the mineralogy and texture strongly influence rock performance, emphasizing the importance of combined petrographic and geotechnical assessments in evaluating stone resources.